1. Field of the Invention
The present invention relates to a generator output controller for an electric vehicle having a generator mounted in addition to a battery.
2. Description of the Prior Art
An electric vehicle traveling by driving a motor is already known, which is advantageous in view of low environmental pollution. However, because the electric vehicle drives the motor using electrical power from a mounted battery, the maximum travel distance of the vehicle is limited due to the capacity of the battery. Particularly, because the weight and the size of a battery are limited by the fact that the battery is actually mounted on a vehicle, the capacity cannot be increased very much, so the maximum travel distance cannot be increased very much either. Moreover, because it takes a long time to charge the battery, it cannot be expected for the state of charge of the battery to recover quickly, although gasoline can be fed to a gasoline-fueled vehicle in a short time. Therefore, a hybrid vehicle is proposed whose maximum travel distance is increased by mounting an engine-driven generator on an electric vehicle and it is possible to charge a battery using electrical power obtained from the generator.
Because the hybrid vehicle drives an engine, it produces exhaust gas. However, because the engine is driven to generate electric power, the load fluctuation and the rotational speed fluctuation of the engine are much smaller than those for driving a vehicle and therefore harmful components in exhaust gas can be greatly decreased.
Therefore, a travel distance equal to that of a gasoline-fueled vehicle and a low environmental pollution close to that of an electric vehicle can be obtained from the hybrid vehicle.
To minimize harmful components in the exhaust gas of this type of hybrid vehicle, it is desirable to drive the engine at a constant load and a constant rotational speed so that the power generation is kept at a constant value.
However, the power consumption of an electric vehicle depends on the travel conditions. That is, when the electric vehicle travels on many upward slopes or repeatedly stops and starts because there are many traffic signals, the power consumption increases. Therefore, it is disclosed in Japanese Patent Application Laid-Open No. SHO-60-7437 (1985) (JP-A-60 007 437) that the electric power output of a generator is controlled in accordance with the state of charge of a battery.
However, if the generator output is changed as described above, the engine output must also be fluctuated. Therefore, a problem occurs that harmful components in exhaust gas increase. Moreover, a problem occurs that the operation of an engine in the above way increases fuel consumption.